let smallPicture = document.querySelectorAll('#smallPicture li img');

console.log(smallPicture);
console.log(document.querySelector('#BigPicture img'));
for (let i = 0; i < smallPicture.length; i++) {
    smallPicture[i].onclick = function(){
        document.querySelector('#BigPicture img').src = smallPicture[i].src
        return false;
    }
}
    